Switch to qemu-img functions from ironic-lib 6.0.0

Change-Id: I0010d8710db4f2859dabe8ccfa5bf478d4f039f6

tools/config/ironic-config-generator.conf

@@ -9,6 +9,7 @@ namespace = ironic_lib.json_rpc
 namespace = ironic_lib.mdns
 namespace = ironic_lib.metrics
 namespace = ironic_lib.metrics_statsd
+namespace = ironic_lib.qemu_img
 namespace = ironic_lib.utils
 namespace = oslo.db
 namespace = oslo.messaging